Graininess—How to Make Less (or More!)

What if your image looks cheap and grainy? Assuming it's not a flaw in
your expensive camera, it might be due to taking a shot in low
light.

Your camera will automatically do its best to make a good exposure in
low light, and the most common way is for it to fire the flash. But
maybe you told it not to fire the flash, so it has to do something
else.

In effect, the camera is able to "do more with less", by sampling light
for a shorter time, and simply being more sensitive to it. (This is
known as "increasing the ISO".) This additional sensitivity, however,
comes at a price.

Image at ISO 100

Image at ISO 1600! Yikes!

As you might have guessed, that price is additional graininess. If you
want more graininess, increase the ISO or lower the light on your
subject. If you want less graininess, decrease the ISO or raise the
light on your subject.

If you can force your camera to use a low ISO setting even in low
light, you can get non-grainy photos there as well. However, to make up
for the low ISO, the camera will want to take a long exposure, and
you'll likely need to put the camera on a tripod to handle it.

Carrying around a tripod for this eventuality can result in some
great photos!

There is one more thing that can cause graininess, and that's the
level of compression used on the image. See the section on JPEG Jaggies.